The moisture content of seeds for sowing, or sowing seeds, plays a crucial role in the quality of these seeds and the control of their deterioration. Despite the fact that this is generally accepted, the technology used for the drying of sowing seeds is mostly still based on circulating heated air streams through the seed lots. The dedicated seed drying equipment available and based on this technology is technologically advanced and costly. With respect to seeds for consumption, also quality characteristics must be preserved in order to preserve taste and nutritional value. For brewing barley, for instance, it is very important that the germination characteristics of the seeds are not diminished by, for instance, fungal attack.
An important consideration in the drying of seeds is that germination capacity and longevity (shelf life) of the seed must be maintained. The germination capacity refers to the percentage of seeds that after a defined period under optimum storage conditions germinate and develop into a full seedling. Germination capacity is determined with a representative sample of the seed. It has been found that the extent of the drying process influences the germination capacity in so far that excessive drying often results in loss of vitality. Insufficient drying, however, results in molding of the seeds when stored. More importantly, each type of seed has its own optimal conditions for drying. It has proven very difficult to produce drying conditions that work very well for a wide variety of seeds.
Although sowing seeds produced by seed companies are generally of a very high quality, the majority of the sowing seeds used in the world are “farm saved seeds”, and their quality differs from season to season. At harvest, moisture content of the seeds is in most cases not optimal and the moisture content within a seed lot is usually not homogeneously distributed due to differences in the field and different levels of maturity of seeds on the plants.
Farm saved seeds or “farmer seeds” are usually stored for several months before they are sown. When stored in countries with a high humidity and high temperatures, 80% of the seeds will be dead or useless in the sowing procedure, and drying is necessary to avoid germination. Large postharvest losses are due to improper drying and germination of kernels. In particular small farmers are in need of suitable seed drying methods in order to improve the quality of stored seeds.
There are presently no methods available with which small farmers in less industrialized areas of the world can properly dry their farm-saved seeds. The available air flow dryers are complex and expensive, and require a relatively high level of skill of the operator. Although central seed treatment facilities may be used, it is mostly far too expensive to transport the farm saved seeds of the bulk crops to central seed treatment facilities. It would be much more favourable to bring the seed treatment facilities to the farmers in order to upgrade the quality of these seeds. This requires mobile systems for seed treatment. In principle, such mobile seed treatment units should be simple and easy to operate in order to support seed treatment of farm saved seeds at farms in second and third world countries. Thus, there is a need for a simple, cheap, robust, efficient and well controllable system for drying seed that is preferably transportable and can preferably even be operated during the transportation of the seeds.